E, t, a, o, and i.
It is possibly the vowels: A I E O and U
There is no special term for this.
T,u, p,i,t,o
It is possibly the vowels: A I E O and U
120.
Z is used 0.07% of the alphabet
The letters j, k, w, x and y are letters that may be described as being in the English, but not the Italian, alphabet. The letters nevertheless do get used since they may be needed for foreign loan words, such as jazz, karaoke, walkie-talkie, xeres and yuppie. Their use introduces five consonants to an alphabet that traditionally preserves five vowels and 21 consonants.
A
These are common letters used to describe the unknown quantity for which you are solving. They can be any letter of the alphabet, it's just that these four letters are the most commonly used ones.
the alphabet
There is no such language as Ourmukhi. If you are talking about the Gurmukhi alphabet, it's used to write the Punjabi language.
A modified version of the Arabic alphabet is used for Persian. It is the 28 letters of the Arabic alphabet, plus 4 additional letters used only in Persian.